I am sure some people have both going on, but more likely its 50/50 or less.
I am not submissive, and I don`t want to be more then a secondary (preferrably less ) role to anyone else.
You will have people who are secondaries or tertiaries due to logistics. They simply don`t have the time for fulfilling primary roles. They happily only engage in secondary or tertiary roles. I can think of a couple of men I know, who are divorced and raising their children. They do not want a 'step-mommy' in the picture. They are not seeking to be, nor desire to have, a primary. Neither are submissive.
I know a female who is poly-oriented, however, makes it clear she only sees her poly partners as secondaries or tertiaries. When the monogamous man, and the white picket fences comes into the picture,..bye-bye secondaries. Essentially she is the 'leader' by design, yet sexually submissive.